Catastrophic failure


Son was riding at night, hit a pothole within the bike lane and the wheel sheered off. I had the same type of 8mm rod bend on me when I hit a bad joint on a sidewalk but I never anticipated the steel would completely sheer. He’s scraped up pretty good but nothing major.

I’m looking for pneumatics with larger bearings - maybe 12 mm and higher strength steel or titanium?

Just don’t think the roads around here are good enough for urethane, even the bigger 110mm…

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Sorry about your son, many run 10mm and 12mm axles nowadays for pneumatic setups so there are options, however a 8mm axle shouldn’t just shear of like that, would assume there was some defect causing that catastrophic failure or just poor metal used.

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You can run 10mm axles in those wheels, just use 6900-2RS bearings instead.

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Titanium isn’t actually any stronger than decent steel. Its only advantage is specific strength, AKA strength/weight, because titanium is less dense.
(Basically I’m saying you don’t need titanium. Good quality steel is just as strong, and a fraction of the cost.)

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I’m fairly sure titanium isn’t actually that strong, it’s just very strong for its weight. Steel axles are the way to go

Edit: fuckin sniped me right at the submit button

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I can’t remember your build exactly, but that looks like threaded rod. I would never trust fully threaded rod to take esk8 loads like that. It is not ideal as a shaft at any sort of high rpm. You’re effectively running 6.6mm (minor diameter for M8x1.25) axles. This is not a wheel dia issue, although that may help you roll over road imperfections better.

Get an 8mm OD or better rotary shaft (hollow or solid) in a good alloy steel, with threaded ends only. You should be able to find what you need on Misumi pretty easily.

How are you getting your bearings to run true on threaded rod? Do you have some sort of threaded spacer? I’d be shocked if you didn’t get tire vibration at high speed if you’re running bearings straight on threaded rod. Eventually the high hardness inner race of the wheel bearings will probably wear flats in the threaded rod, unless you specifically chose a high hardness rod.

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Don’t use threaded rods for axles, they are only really made for tensile stress. Use an actual shaft like @sleepless already said. Shoulder bolts with their heads cut off are a good alternative if you can’t find any.

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that axle is like perforated paper :flushed:

I’ve got 8mm sleeves over the threaded rod and am using 10 mm bearings over the sleeves. I went with a 16mm threaded rod for the second build an am looking to change out to pneumatics for the first build and use 12mm bearings. I’ve had a hard time finding partially threaded rods that work, but definitely not going to use 8mm rods again. Thanks for the input.

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Can you use double ended studs? It wouldn’t go all the way, but it looks like you have some sort of mating block anyways you could thread into.

image

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Maybe a quick solution?

I’ve prototyped a few truck versions using 1/2” OD, 0.12” wall tubing that I threaded to accept grade 10.9 M8x1.25 bolts as axles.


If those hexagonal shaft collars you have there are already bored out to 1/2”, this would be a simple stop gap fix for ya.

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Thanks guys. I’ll sketch up some from your ideas in Fusion tomorrow and see what works!


Using a 12m-1.75 150mm double ended threaded stud from Grainger may work. I’ll probably need to mill a new coupling which isn’t an issue because as-is, the stud will only thread into the coupling for 10-11mm. I’m guessing I’ll want it seated more than that into the coupling - perhaps 16-18mm? The coupling is 6061 aluminum. I think that will be strong enough to prevent bending and such within the aluminum from the stresses on the stud? I’m anticipating using the Group GT3 wheels from @Boardnamics with the 12mm bore. A 25mm aluminum spacer after the initial hex nut should provide spacing for the wheel and pully combo. And the outer threads should let me put pressure onto the bearing washers to keep the wheel in place… Fairly cheap solution if it’s strong enough…

What about the BN axles? They’re 10mm, but they’re sized more properly for wheels with a much larger shoulder.

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Just curious, using MBS wheels with a 38.2mm contact width as an example, why such a large shoulder?

I think it’s for the pulley bearing. There’s also a 10-8 stepped version as well. Someone with BN270s could comment more on it, since I’m not too sure myself.

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